IE9 Release Candidate, or RC, is the final preview before Microsoft gives the code the green light sometime before the end of March. The company shipped IE9 RC last Thursday.

According to a pair of Microsoft program managers who announced IE9 RC's distribution on a company blog, the new build was to have reached a limited number of users Monday.

"This rollout will start with a narrow audience and expand over the next few days to cover all Internet Explorer 9 beta users," the company said.

As it did with both IE8 and IE7, Microsoft will give IE9 beta users the option of rejecting or delaying the installation of the RC. Users will see a splash screen before IE9 RC installs that gives them three choices: "Ask me later," "Install" and "Don't Install." Users who pick the first option will see the upgrade offer after the next update session.

Only users running IE9's beta will see the automatic offer. Microsoft recently claimed that 25 million copies of the beta had been downloaded since September 2010.

At some point after the final release of IE9 -- Microsoft calls the milestone "RTW," for "release to the Web" -- the new browser will be offered to all Windows Vista and Windows 7 users, who have either IE7 or IE8 on their machines. If Microsoft repeats the timetable it used two years ago when it last upgraded the browser, it will kick off the IE9 updates to Vista and Windows 7 about six weeks after announcing RTW.

Windows XP users will see neither the IE9 RC or IE9 RTW offers because the browser does not work on the still-dominant operating system.

Microsoft has yet to set a date for IE9's final release, but has promised to ship the browser this quarter.

In preparation for the day when IE9 RTW lands on Windows Update, last week Microsoft also published a blocking toolkit for IT administrators who want to keep the new browser off company machines.

Microsoft rolls out such blocking kits -- which include executable scripts and Group Policy templates -- prior to delivering major upgrades to its operating systems and browser. Last November, for instance, Microsoft published a blocking kit for Windows 7 Service Pack 1 (SP1), the OS upgrade the company will add to Windows Update on Feb. 22.

IE9 is Microsoft's latest attempt to entice expatriates to return. According to Web analytics company Net Applications, IE's usage share is down by nearly a third since November 2007; last month IE accounted for 56% of all browsers, a historic low.

Users can obtain the IE9 release candidate from Microsoft's Web site. The 32-bit version weighs in at just over 19MB, while the 64-bit version is a 37MB download.